1. Field of the Invention
This invention is related in general to the field of equipment for controlling the distribution of weight on haulage trucks and, in particular, to a system for placing the center of gravity of a load at a predetermined desired spot on a truck bed.
2. Description of the Related Art
Surface mines utilize large haulage trucks for moving material from the mine pit to processing plants and waste disposal areas. These trucks operate back and forth between loading and discharge points over roadways in and around the mine pit, repeatedly carrying as much as 400 tons of material. The trucks are designed to promote the even distribution of the material loaded onto them irrespective of whether they are loaded from the front, sides, or back of the bed. The bed geometry includes sloped walls and a tilted bottom that effectively reduce the natural angle of repose of the material loaded so that it will flow to a relatively uniform pile. As in the case of conventional trucks, the weight of the load is typically distributed over four or more wheels located approximately at the corners of the truck bed for stability and convenience.
Most work machines that are used for loading trucks, such as excavators, shovels, backhoes and the like, are human-operated, mobile pieces of equipment constantly being moved around on the surface of the mine. Skilled operators ensure that the machine is positioned in the right place and is optimally oriented to perform its intended function. For example, an excavator operator will ensure that the undercarriage of the machine is sufficiently close to the minable seam and that its; boom is oriented so as to permit the bucket of the machine to reach and extract a full load of material, and to reach a haulage truck positioned for receiving the load. Similarly, a truck operator will ensure that the vehicle is within the comfortable and safe reach of the excavator's boom.
During normal mine operation, each truck is loaded by placing it under the bucket of the shovel or other mining equipment, such that its contents can be released directly onto the truck's bed. Typically, at least three bucket loads are required to fill the bed to capacity. Therefore, depending on the position of the bucket with respect to the truck's bed at each loading step, the loaded material may be distributed unevenly in spite of the truck's design. Since it is known that an uneven load may cause excessive wear of a tire and/or non-uniform wear among the sets of tires in service on a given truck, it is desirable to spread the load as evenly as possible. Furthermore, with the advent of operator-less equipment, information about load distribution will also be useful for determining the optimal placement of material by automated on-board shovel-control system.
Haulage trucks utilize very expensive oversize tires that are rated and maintained on the basis of tonnage and speed; that is, tire ratings are expressed in terms of expected ton-mile/hour or tmph. The tonnage, mileage and speed of operation of each truck are recorded for maintenance purposes and the tires are routinely replaced when their tmph rating is reached. Obviously, such timely replacement is not only an issue of proper maintenance but, given the size of the loads carried and the conditions of the roads traveled, it is also a safety concern. Therefore, the condition of truck tires at all times is very important to a mining operation.
In order to address some aspects of this problem, monitoring systems have been developed to track the loading and haulage operation of surface mining vehicles. For example, U.S. Pat. No. 5,528,499 and U.S. Pat. No. 5,631,832 describe systems for processing data derived from the weight of a load carried by a haulage vehicle. These systems include pressure sensors distributed under the bed of the vehicle to detect the weight of a load for deriving data indicative of hauling conditions. Historical as well as current data are used to formulate management decisions regarding future operations intended to achieve a predetermined management goal.
The prior art does not disclose a system for affecting the load distribution on a haulage truck being loaded. Therefore, known methods and apparatus are not suitable for providing an even distribution of the load placed on a haulage truck bed, as required to minimize tire wear and ensure safe operation of the haulage vehicles in a typical mining environment. The present invention provides a procedure and an apparatus that overcome these deficiencies.